In REXX expressions, blank space is interpreted as an implicit concatenation operator -- the terms are concatenated with a blank in between. As a result, REXX will interpret many mistyped statements as an expression involving the blank concatenation operator.

For example, inserting a blank after a function name in a function call changes the meaning of the expression from:

text_upper = translate ( text )
to
text_upper = "TRANSLATE" || " " || text

Blank space also plays a special role in the PARSE instruction. Compare the following:

parse arg a b c

parse arg a, b, c

The first line parses the first argument passed to the routine into three parts, while the second line sets the three variables to the value of the first three arguments passed to the routine.